The present invention relates to an illumination light source provided with light-emitting diodes.
A light-emitting diode (referred to below as “LED”) is a semiconductor device that can produce an emission with a brilliant color and high efficiency in spite of its small size.
The emission produced by an LED has a high color purity because of its narrow spectral half-width. Recently, blue LEDs have been put to practical use, so that LEDs are now available in the three colors red, green and blue, which makes it possible to produce white light with the LEDs.
In the prior art, LEDs have been mainly applied to display devices. For that reason, the use of LEDs as a light source for illumination purposes has not yet been researched and developed sufficiently. When LEDs are used for a display device, just the light emitted spontaneously from the LEDs should have its properties optimized. However, where LEDs are used in combination as the light source for illumination purposes, the white light, with which an object will be illuminated, should have its color rendering performance adjusted as well. In the current state of the art, LED illumination light sources with optimized color rendering performance have not yet been developed.
LEDs have excellent monochromaticity. Accordingly, if white light produced by LEDs is to be used as illumination light, this high color purity and the material characteristics that are unique to LEDs may cause various problems regarding, for example, the problem which distribution spectra to include in the LED light sources in order to obtain white light that is suitable for illumination, or the problem which luminescent materials to use for the LEDs, since the emission spectrum and the luminous efficacy may vary depending on the luminescent material of the LED.